In recent years, light-emitting portions using semiconductor light-emitting elements, such as light-emitting diode (LED) chips, have been suggested for the application in vehicle headlamps (see Patent Literature 1).
The light-emitting device described in Patent Literature 1 has a light-emitting portion that includes an LED chip and a wavelength converter encapsulating the LED chip. The wavelength converter is made of a transmissive material containing yellow phosphor particles. The wavelength converter converts part of blue light emitted from the LED chip into yellow light. On the other hand, the rest of blue light emitted from the LED chip passes through the wavelength converter without being converted into yellow light. As a result, the light-emitter emits white light results from the mixture of blue light and yellow light.
FIG. 20 is a view explaining the light distribution characteristics of such a light-emitting device.
A light-emitting device 2001 has a light-emitting portion 2020 that includes: an LED chip 2022 mounted on a mounting substrate 2011; and a wavelength converter 2024 having a dome shape and encapsulating the LED chip 2022. The LED chip 2022 is a so-called a blue LED that emits blue light. The wavelength converter 2024 is made of a transmissive material (such as silicone resin) containing yellow phosphor. The length of optical path that light emitted from the LED chip 2022 travels within the wavelength converter 2024 is substantially constant irrespective of the emission directions. With this arrangement, the color temperature of light emerged from the light-emitter 2020 is all uniform irrespective of the emission directions.
As shown in the portion (a) of FIG. 20, suppose that the screen SC is disposed at a location away from the light-emitting device 2001 in the direction of the optical axis J (in the light emission direction) of the light-emitting device 2001 such that the surface of the screen SC is perpendicular to the optical axis J. Then, as shown in the portion (b) of FIG. 20, light emitted from the light-emitting device 2001 irradiates the irradiation area SA31 (hatched area in the figure) on the surface of the screen SC.